Battery Ageing Model

[JejuSoul]

.... When Volts don't degrade it's because...they haven't had enough EV miles even though the packs are as old or older than the Leafs' and exposed to the same high Phoenix temps......

There is a really good discussion comparing the Volt and Leaf batteries on the Spark EV forum.http://www.mychevysparkev.com/forum/viewtopic.php?f=7&t=4030&start=10
The best comments are by Tony Williams below.

We don't actually know how the Volt batteries are doing, .... The only thing that we do know for sure is that GM:
1) Was uber cautious with the amount of capacity that was able to be used, and for VERY good reason. The chemistry that GM selected is precisely the same chemistry that Nissan used in the LEAF.
2) Very wisely made the Volt battery liquid cooled, while the LEAF has no cooling system whatsoever.
3) Used, in my opinion, a far better anode
That's it. Smart, logical choices.

I also talked about the Volt data on the AVTA site a few weeks ago -

The Volt does do much better then the LEAF in Phoenix Arizona. Active cooling clearly works in a very hot climate. But if you compare the deterioration for the EV miles driven the Volt does no better than other Lithium Ion batteries not in Phoenix. I was curious to see if LG Chem's battery was better than SK Inno's. The Volt, Bolt and Ioniq will all be LG Chem. The Soul EV is SK Inno. I see no difference in the data.

 

[Birkeland]

New change in my deterioration data:

Min det: 0.7%
Max det: 9.0%
CED: 4090kWh
CEC: 4200kWh

This happened at about 21.000km.

 

[JejuSoul]

Birkeland: Thanks for the latest numbers. The BMS values fluctuate quite a lot so I prefer to average out these figures over a few months. Your car is the best of those measured so far, but the difference is well within any margin of error. My car has done 17,000km and has max det 7.0%, min det 1.7%. So our cars are the same age and have the same deterioration, but you have driven 4,000km more. Whereabouts in Norway do you live? The best car on the Nissan Leaf Plugin America Survey is from Trondheim Norway. see http://www.pluginamerica.org/surveys/batteries/leaf/vehicle.php?vid=510 I assume that if you live closer to the Arctic Circle your deterioration will be less. Has anyone ever checked this in Norway?

Here's a graph of the latest Soul EV BMS deterioration data.

For comparison here is the same chart with Renault Zoe BMS data from http://canze.fisch.lu/battery-health-status/
The trendline is almost identical.
I deliberately did not put these two on the same chart because the way deterioration is measured is not the same.
I do not expect our values to be very accurate, but they are the best we've got until we find a better way to measure SOH.
The point is to show that they are similar, and that both are wildly different from 'official' data.

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Here is a graph showing the cycle life lab testing of 6 SK Innovation cells for the U.S. Advanced Battery Consortium.

"Cycle life and calendar life estimation were carried out using more than 10 months of life data. Initial results indicate that when LMO-free E400 takes a purely drive mode, it can run more than 248,000 miles based on 80% of capacity retention."

To find this data follow the links in post 1 at the Comparing Battery Chemistries thread - http://www.mykiasoulev.com/forum/viewtopic.php?f=14&t=565

 

[ZuinigeRijder]

My deterioration numbers improved again:

Previous:

Date	         km	Max Det	Min Det	Max Cell	Min Cell	CEC	CED
2016-04-15	24876	10.2	8.7	43	15		5132	5020

Now:

Date	         km	Max Det	Min Det	Max Cell	Min Cell	CEC	CED
2016-05-06	26478	8.8	7.3	2	8		5408.2	5286.5

This time I have driven till turtle mode. There was 3.5 % remaining on the display (5% BMS).

The worst numbers I have seen since I have the OBDII dongle are Max 13.7 and Min 12.1

 

[Birkeland]

Birkeland: Thanks for the latest numbers. The BMS values fluctuate quite a lot so I prefer to average out these figures over a few months. Your car is the best of those measured so far, but the difference is well within any margin of error. My car has done 17,000km and has max det 7.0%, min det 1.7%. So our cars are the same age and have the same deterioration, but you have driven 4,000km more. Whereabouts in Norway do you live? The best car on the Nissan Leaf Plugin America Survey is from Trondheim Norway. see http://www.pluginamerica.org/surveys/batteries/leaf/vehicle.php?vid=510 I assume that if you live closer to the Arctic Circle your deterioration will be less. Has anyone ever checked this in Norway?

I live in the southern most part of Norway. Trondheim is further north. There has not been, to my knowledge, any studies (unoficially or otherwise) of deterioration based on geography in Norway. But if you look at the table 1/3 down this page http://www.electricvehiclewiki.com/Battery_Capacity_Loss, you will see: "Rygge, Norway" being very favorable when it comes to degradation of Nissan Leafs battery compared to the rest of the world. The annual average temperature where I live is 10.5 degrees Celsius. It is no doubt colder climate is better for the battery then hot places, but the cold weather also means more energy used on the battery heater and on heating the cabin. So we usually get less milage pr kWh. And the number of kWs put in and drawn from the battery (number of cycles) will also affect the deterioration. But for the time being, it seems the cold climate wins over number of cycles.

 

[JejuSoul]

But for the time being, it seems the cold climate wins over number of cycles.

It didn't last long. The deterioration numbers on my car have fallen again. I am now max 7.5% min 0.5%. So there is no longer any difference between our cars. The only factor that is visibly influencing deterioration in our numbers so far is distance driven. That my numbers have fallen is not a calibration effect. I have only charged to 80% and never gone below 20% in the last month.

Also the fact that a Norwegian N issan L eaf is the best in the PluginAmerica survey is significant because almost all of the respondents are from America. In our data Norwegians are in the majority. No surprise because there are more Soul EVs in Norway than anywhere else. Hence there would be no significance if just one Norwegian car happened to be the best, when other cars in Norway were just average. At the moment GoEVs car is slightly less than the average, which means the Norwegian average is in the middle.

 

[2016Electric]

I've been giving this topic some thought lately... and I think there's something wrong with the way degradation has been calculated.
I am assuming the min and max values for best and worst cell are being used, since we don't have SOH. Seeing that there are what? 96 cells? That means that we only have the values for 2/96 cells... 94 cells are UNKNOWN at any given point in time.
The problem is, we don't know how representative the sample group is of the other 94 cells... also, 2 data points is far too small a sample to be meaningful to determine overall pack health.
For example, say we know max is 9% and min is 1%... am I correct in assuming we are simple calculating an average between these of 5% for the purposes of this thread/model?

If so, that can't be right, because we don't have any weighting for the values. 95 of the cells could be at 1% and only 1 at 9%. What we NEED is individual degradation figures for each of the 96 cells. Knowing the pack is 30kw out of factory, and assuming % degradation of a cell is representative (and linear) of the lost wattage capacity of that cell:

30/96 = 0.3125 kW/hr per cell (new)
Multiply 0.3125 by (1 - lost cap %) for each cell
Sum the total of the 96 values
Summed total / 30 = SOH


So the questions are, do with have the PIDs needed to query individual cell degradation?
And.. how reliable is that degradation Stat given that it tends to jump around?

 

[JejuSoul]

On my own car's deterioration values, last week was a setback, when they got worse 3 times that week. They are now 10.8%/9.4%, up from 7.9%/6.5%. I think maybe this has to do with the highway-ish driving to the dealer, which is 2x100km and mostly CC at around 100km/h. My everyday work commute is more varying and 40-80km/h, so the deviant driving pattern might have triggered the change. Maybe..

I have just seen the same. My car's deterioration values got worse twice this week after a much faster and steeper than normal drive. (The freeway over the mountain.) My everyday work commute is more gentle, flat and 40-80km/h, so the deviant driving pattern might have triggered the change. Again maybe! I am now 9.5%/2.1% up from 7.5%/0.5%

2016Electric: Yes. I am just averaging the two values to get a proxy value for the average of all 96 cells. You arguments why this is a dubious method are justified. But we do not yet have a better way. No one has yet to see how to read the actual SOH value. The fact is that despite only having data for 2 of the 96 cells we get statistically significant consistency once the sample size is large enough. For any single car averaging the values over time forms a stable trend despite single readings yo-yoing around. So far the only effect visible in this data is that deterioration increases with use. We do not see any effect for climate, charging style or driving style.

A different and probably more reliable way to measure deterioration would be to perform a Tony William's style range test each year. It wouldn't be very exciting because up until now all of us would have seen no significant loss of range. We'd have to wait another year before we start getting any interesting data.

 

[2016Electric]

On my own car's deterioration values, last week was a setback, when they got worse 3 times that week. They are now 10.8%/9.4%, up from 7.9%/6.5%. I think maybe this has to do with the highway-ish driving to the dealer, which is 2x100km and mostly CC at around 100km/h. My everyday work commute is more varying and 40-80km/h, so the deviant driving pattern might have triggered the change. Maybe..

I have just seen the same. My car's deterioration values got worse twice this week after a much faster and steeper than normal drive. (The freeway over the mountain.) My everyday work commute is more gentle, flat and 40-80km/h, so the deviant driving pattern might have triggered the change. Again maybe! I am now 9.5%/2.1% up from 7.5%/0.5%

2016Electric: Yes. I am just averaging the two values to get a proxy value for the average of all 96 cells. You arguments why this is a dubious method are justified. But we do not yet have a better way. No one has yet to see how to read the actual SOH value. The fact is that despite only having data for 2 of the 96 cells we get statistically significant consistency once the sample size is large enough. For any single car averaging the values over time forms a stable trend despite single readings yo-yoing around. So far the only effect visible in this data is that deterioration increases with use. We do not see any effect for climate, charging style or driving style.

A different and probably more reliable way to measure deterioration would be to perform a Tony William's style range test each year. It wouldn't be very exciting because up until now all of us would have seen no significant loss of range. We'd have to wait another year before we start getting any interesting data.

Hmm. So no PIDs. Yet.

Range test sounds viable, but there are so many factors that would be hard to adjust for. Traffic and wind being two that come to mind, even if route and driving style could be accounted for.

I wonder if a more accurate (although tedious method) would be to apply a static load to the batter from 100%.
- charge to 100
- measure kw CH and dischg
- crank the hvac and walk away
- stop at 10%
- measure kw CH and dischg
- chg to 100
- measure CH and dischg

Then Calc how kw were burned running the battery down 90, and interpolate the remaining 10%.. should give a pretty decent idea what the battery is capable of putting out. Tedious but might work.

 

[Elmil]

On my own car's deterioration values, last week was a setback, when they got worse 3 times that week. They are now 10.8%/9.4%, up from 7.9%/6.5%. I think maybe this has to do with the highway-ish driving to the dealer, which is 2x100km and mostly CC at around 100km/h. My everyday work commute is more varying and 40-80km/h, so the deviant driving pattern might have triggered the change. Maybe..

It did improve again after I got back to the normal daily use. It changed to 9.3%/8.2% 10 days later, but since I've now got back to 80% charging, I don't expect any more changes until next time I charge to 100%.
Can anyone explain why the deterioration values changed from 0.0/0.0 to Max=0.5%/Min=1.4% on the brand new loaner car I got? (See earier post on this thread, april 17). It doesn't make sense that the Minimum number is greater than the Maximum number.. Again, I have to question the interpretation of these 'Deterioration' numbers. I know that these names are present even in screenshots from the Service manual, but seeing the behaviour it might as well be someting like 'DTE Calibration Offsets' because, direct or indirect, they affect the estimated driving range displayed.
Seems odd that an actual deterioration of a battery cell could be reversable..

I wonder if a more accurate (although tedious method) would be to apply a static load to the batter from 100%.
- charge to 100
- measure kw CH and dischg
- crank the hvac and walk away
- stop at 10%
- measure kw CH and dischg
- chg to 100
- measure CH and dischg

Then Calc how kw were burned running the battery down 90, and interpolate the remaining 10%.. should give a pretty decent idea what the battery is capable of putting out. Tedious but might work.

Clearly it's a way to go, although tedious.. At least you would remove the recuperated energy from the equation.

You might also consider measuring the Cumulated Amperage counters instead. This gives several benefits:
- A battery's State Of Charge is normally rated in Ah. Could match the SOC% reading better.
- Removes some of the temperature and load dependencies.
- Offers ~2.8x better resolution.

In early spring I did a calibration cycle by charging to 100%, driving to 3% and charging to 100%. The result:

Discharge (97%) 72.0Ah 25.1kWh
Charge    (97%) 72.0Ah 26.1kWh

My Ah counters are today: Ah In - 16380.7 and Ah Out - 16343.1 at 60% SOC. Very accurate.

 

[JejuSoul]

Seems odd that an actual deterioration of a battery cell could be reversible.

The deterioration numbers that we see are created by an algorithm in the BMS. They are not 'real' values. From the limited data we have it seems that the BMS makes better guesses when the car is charged to 100% and when the temperature is closer to 20C.

We have already discussed this issue in the Battery Calibration thread - http://www.mykiasoulev.com/forum/viewtopic.php?f=14&t=444&p=2684#p2684

In that thread I link to this page on the Battery University website. - http://batteryuniversity.com/learn/article/battery_calibration

Here is a quote from that page

There is often a false sense of security in believing that the displayed battery readings are correct. Fuel gauge displays can be made fancy and believable but the truth is only as good as the information provided.

Also interesting is this page. - http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

Makers of advanced BMS claim high accuracies but real life often shows otherwise.

 

[JejuSoul]

My Ah counters are today: Ah In - 16380.7 and Ah Out - 16343.1 at 60% SOC. Very accurate.

Can you explain what you mean when you say this is very accurate, and how we would use this to get an idea of the deterioration.
Do you know if you have any deterioration in usable capacity.?

On the Battery University web page linked above is this this quote

Of special interest in terms of battery state-of-health (SoH) is full charge capacity (FCC), .... FCC can be used with reasonable accuracy to estimate battery SoH without applying a full discharge cycle to measure capacity.

 

[Elmil]

My Ah counters are today: Ah In - 16380.7 and Ah Out - 16343.1 at 60% SOC. Very accurate.

Can you explain what you mean when you say this is very accurate, and how we would use this to get an idea of the deterioration.
Do you know if you have any deterioration in usable capacity.?

I'm just looking for an easy, reliable way to measure and compare the battery capacity of my car. Getting rid of the Voltage variable makes sense.
The Voltage/kWh measurements are fluctuating more depending on load and temperature, and there is also the low resolution of the kWh counters.
My battery has supplied almost exactly the same number of Ah as it has received, so my point is that the capacity in Ah:s could be measured eather way, charge or discharge, but the kWh:s are always including unknown losses.

I still don't see any signs of decreased useable capacity (after 34000km). The range estimations as well as real driving range are back after the winter. 100% displayed SOC is always 95% of battery. On the lower side, when I drained it to 3%, the battery was at 4.5%, so maybe there is a drop there, but on the other hand I don't have any numbers from when the car was new.

 

[JejuSoul]

I still don't see any signs of decreased useable capacity (after 34,000km).

Good. The battery in the Soul EV is holding up well so far. None of us who are measuring deterioration have yet to see any range loss.

...the kWh:s are always including unknown losses...

True - that is the second law of thermodynamics.

The Advanced Vehicle Testing facility in Phoenix is now publishing battery efficiency data. Although the Soul EV data isn't up yet. Here is the data for the BMW i3.

Comment 16 explains the oddity of 102% efficiency in terms of the quirks of the proprietary algorithms of the BMS

16. In some charging event instances, the amount of electrical energy can be less than the amount of energy that was discharged.  The amount of energy that is allowed to be input to the ESS is determined by the vehicle battery management system (BMS), and factors such as ESS state of health and temperature, as well as ambient temperature are used in the proprietary algorithms of the BMS.  The battery roundtrip efficiency being greater than 100% is a result of the BMS allowing less energy to be input in the subsequent charge event than it allowed to output during the range test.

 

[Birkeland]

I came across a couple who had just got their new KIA Soul EV a week ago. I asked politly if I could take a reading of their battery data. I was surprised to see the deterioration numbers. If my memory serves me right, they had 649km on their odometer.

 

[JejuSoul]

I came across a couple who had just got their new KIA Soul EV a week ago. I asked politly if I could take a reading of their battery data. I was surprised to see the deterioration numbers.

I bet it was hard to explain to them why their brand new car looks to have such a high deterioration.

This isn't the first excessive negative outlier. There was a similar report from Switzerland about 5 months ago. That car now has above average readings. Search the German forum in the OVMS thread if you want to see the details. It is hard to explain all the quirks of the proprietary algorithms of the BMS. I have always included the outliers in the data collected here. Look back at page 3 of this thread; my comment dated Mon Jan 18, 2016.

 

[Elmil]

After several improvements during one week, I am now at the lowest deterioration values since first measurement 8 months ago.
Max/Min deterioration is now 7.7% / 6.3% after 35000 km.

 

[JejuSoul]

I am now at the lowest deterioration values since first measurement 8 months ago.

This is good. Sweden is now leading the race. My car is doing well - 19,251km, max 8.5% min 0.4% but I am still 3rd behind Birkeland in Norway.
Top 3 in the distance travelled before 70% deterioration of usable capacity.

Elmil - Sweden - 200,000km
Birkeland - Norway - 173,196km
JejuSoul - Korea - 173,043km

Still a long way to go though, and perhaps (probably?) deterioration will get less with age (this projection assumes linear). All these cars are only a year old so we don't know what will happen yet. Also note none of these cars have any deterioration of usable capacity at all yet. (Elmil are you still at SOH 100%)

 

[Elmil]

(Elmil are you still at SOH 100%)

I really don't know.. Don't see why it shouldn't though..
When I had service #2 after 30000km the guy who did it the first time was home sick, and whoever handled my car didn't know how to print the battery report.. Embarrassing..

I think my time in the sun was short - had a few more ups and downs the last 2 weeks, and currently I'm at 9.2/8.2. Here's my whole list:

DATE	     Km	     Max   Cell	 Min   Cell
2015-11-01           9.3%   32     8.3%    1
2015-11-05  18780    9.8%    2     8.4%    8
2015-11-19  19751   10.3%   24     9.2%    1
2015-12-23  22610   11.2%    3    10.2%    8
2016-02-29  27339    9.8%    2     8.8%    8
2016-04-04  30209    7.9%   37     6.5%   20
2016-04-12  30871    8.3%    2     7.3%    8
2016-04-13  31073    8.4%    4     7.0%    8
2016-04-15  31291   10.8%   44     9.4%    8
2016-04-25  31934    9.3%    2     8.2%    8
2016-05-24  34405    9.0%   45     8.0%    8
2016-05-26  34637    8.6%   26     7.6%    8
2016-05-31  35159    7.7%    2     6.3%   20
2016-06-03  35502    8.3%    2     6.8%   20
2016-06-10  36851   10.4%    1     9.3%   68
2016-06-11  37016    8.0%    2     7.0%    8
2016-06-15  37432    9.2%   37     8.2%    1

I made a road trip of almost 1000km between the 3:rd and the 6:th, including several QC:s. Probably a reason for the increase. Note also how some 'cells' are frequent, and I think particularly interesting is cell #1, appearing as worst at 36851km and then it's the best only 581km later..

 

[JejuSoul]

My latest deterioration data has jumped again. Latest numbers - 20,020km max 8.5% min 6.0% Perhaps this marks the end of Spring. I have done no major drives recently and have not charged to 100% for the last 2 months. So perhaps this is the BMS losing calibration. I have fallen way behind the Scandinavians in the leadership race. Norway is now leading, Sweden second.

Here's a chart showing trendlines for the data collected so far . Top is Birkeland, 2nd Elmil, 3rd JejuSoul.